This invention relates generally to the field of wireless communication. More particularly, in certain embodiments, this invention relates to a system which overlays one-to-many Dispatch functions onto radio telephone systems.
Many traditional land mobile radio systems provide a mechanism for establishing a one-to-many talkgroup function wherein members of a talkgroup can communicate with one another in a simplex communication arrangement. In such an arrangement, for example, any member of the talkgroup can communicate with other talkgroup members by pressing a Push-To-Talk (PTT) switch and speaking. All other members of the talkgroup are able to hear the communication and can follow up with responses, which operate in a similar manner. In these traditional land mobile arrangements, subscriber selection and participation in a particular desired talkgroup, while excluding participation in undesired talkgroups, and security and Authorization for allowing participation in any particular talkgroup, is handled by a variety of mechanisms ranging from simple RF frequency selection/carrier squelch, PL (Private Line(trademark) subaudible tone signaling), DPL(trademark) (Digital Private Line data under voice), to digital identification codes.
In the more telephone connection-oriented radio systems, like AMPS (Advanced Mobile Phone Service) Cellular, or particularly PHS (Personal HandyPhone Service) or DECT (Digital European Cordless Telephone) digital Time Domain Multiple Access (TDMA) systems, the model for communication has traditionally been one-to-one, having some (perhaps lengthy) processes for selecting the desired call destination, obtaining services from a serving Cell Station (or Control Center Station), and excluding service from those not authorized. Generally these more modern systems offer the user and the system operator a richer set of convenience or security features, such as Caller ID or voice scrambling, with these richer features often coming with the benefit of increased battery life due to synchronous Paging protocols. One of the problems with adding a xe2x80x9cDispatchxe2x80x9dxe2x80x94like function to these traditionally telephone oriented systems is that most of these improvements have come at the cost of increased call setup time and transmission overhead when compared to traditional Land-Mobile radio systems. A one-to-one telephone call is expected to take longer to set up than a quick Push-To-Talk Dispatch call. A single telephone user may only need to register with the system infrequently in order to inform the system of the individual""s presence. But, a Dispatch user may need to handshake with the system for participation with every different talkgroup, or upon selecting a different set of talkgroups. Also, many of the features intended for one-to-one connections, particularly voice scrambling key exchanges and synchronization, become unworkable or unsecure when applied in a one-to-many model. Also, the xe2x80x9cone-shot handshakexe2x80x9d nature of a one-time telephone call setup is not adequate for setting up and continuing a one-to-many call, where multiple receivers may need to be gathered, or come into or out of the call at varying instants.
Thus, there are many problems associated with trying to impose a one-to-many talkgroup protocol over a TDMA cellular type telephone communications model. However, it would prove advantageous to overcome these problems to provide a convenient call setup, late joining, resuming and teardown protocol to accomplish such dispatch-like communications over a wireless telephone network such as the Japan PHS system.